1. Field of the Invention
The present invention concerns a micro-wave tuned oscillator with ultra-low phase noise. Application includes counters, timers, receivers, or waveform generators and a host of other devices that can be found for example in communication devices, modern computers or their peripherals to name a few.
2. Description of the Related Art
The choice of tunable resonance phenomena benefiting from very large quality factor Q is very limited in the microwave frequency range. Ferromagnetic resonance has been found the best tuning element for microwave oscillators. There are several reasons which explain this preference: one benefits both from the large electronic magnetic moment (as opposed for example to nuclear magnetic resonance, where the Bohr magnetron is 3 order of magnitude weaker) and a saturated magnetization at low field (as opposed for example to para-magnetic resonance which requires very large external field). Thus it ensures that the amplitude of the effect is large. The tuning element is the external magnetic field applied on a ferromagnetic sample through a coil. Another important aspect is that the linewidth is almost independent of the uniformity of the external polarization field. The intrinsic linewidth is thus easily observed. At the moment, the best reference material is a monocristal of ultra-pure yttrium iron garnet (YIG) polished to a perfect sphere. The linewidth there is only limited by the magneto-elastic coupling, called the Kasuya LeCraw mechanism, which is of the order of 0.02 G/GHz.
The scientific literature about YIG-tuned oscillators is very abundant and there are numerous patents on the subject. Preceding publications pertinent to the present invention include Japanese patent No. 53-32671 or U.S. Pat. No. 6,348,840 which describes a high Q YIG-tuned oscillator using a spherical sample. U.S. Pat. Nos. 4,626,800 and 4,887,052 which take full advantage of a microwave integrated circuit (MIC) technology by replacing the sphere with a thin film can also be mentioned. The YIG sample can be patterned as a disc as described in U.S. Pat. No. 4,626,800 without deterioration of the Q.
The present invention takes advantage of the non-linear behavior of a ferromagnetic material such as YIG. This aspect has been addressed in the following publications: H. Suhl, J. Phys. Chem. Solids 1, 209 (1957) and H. Suhl, J. Appl. Phys. 30, 1961 (1959). The literature on parametric excitations is very limited. One work on the subject is reviewed in the following paper: W. Jantz and J. Schneider, Phys. Stat. Sol. (a) 31, 595 (1975).